In one known prior art system, an employee's pay details are provided in a two-ply envelope in which the bottom layer takes a carbon imprint from an impact printer which strikes the top layer. To access the pay details, the employee separates the top layer from the lower layer and retains the lower layer which bears the carbon imprint.
Prior art envelopes formed from a folded sheet are known from European Patent Application 302,796, Australian Patent Application 20893/92, European Patent Application 568,266 and French Patent Publication 2,400,465.